JP2007045941A - Method for producing friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a friction material that can satisfy both of prevention of fading phenomenon and improvement of productivity and production cost as well. <P>SOLUTION: In the method for producing a friction material comprising theremosetting resin binding material, reinforcing fiber and friction-conditioning material, these materials are thermally formed, then heat-treated in heated air, further heat-treated in superheated steam atmosphere. The heat treatment under the superheated steam atmosphere is preferably carried out at a treatment temperature of 180°C to less than 800°C for a treatment time of 15 minutes to 1 hour. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a friction material used for industrial machines, railway vehicles, luggage vehicles, automobile friction sliding materials, and the like, and more particularly, to an automobile brake friction material having excellent friction characteristics (fading resistance).

  Brake pads for automobiles use friction materials that are made of organic fibers, metal fibers, ceramic fibers, etc., and are thermoformed using fillers, friction modifiers, and thermosetting resins such as phenolic resins as binders. However, a decomposition product is generated due to the temperature rise of the friction surface, and a fade phenomenon occurs in which the friction coefficient decreases.

In order to prevent this fade phenomenon, a friction material manufacturing method has been proposed in which a part of a binder is carbonized by heat treatment at a high temperature in a non-oxidizing atmosphere to form a thermally stable carbonaceous material. According to the friction material manufactured in this way, since there is little generation of decomposition products when sliding at high temperatures, it is said that the fade phenomenon is less likely to occur and stable characteristics can be obtained.
In Patent Document 1, a molded body containing a fiber base material containing 0 to 10% by volume of an organic fiber, a friction adjusting material containing 0 to 5% by volume of an organic substance, an inorganic filler, and a phenolic resin binder is used. In a non-oxidizing atmosphere using an inert gas such as that described above, a technique for reducing the bubble rate to 25% or less by heating and baking at a treatment temperature of 350 ° C. to 700 ° C. is disclosed.

In Patent Document 2, a filler, a fiber reinforcing material, and a resin containing a dihydrobenzooxy ring in a structure are mixed, and a molded body is formed by heating and pressurizing with a molding machine. A technique is disclosed in which heat treatment is performed in a non-oxidizing atmosphere using an inert gas such as carbon under conditions where the processing temperature is 250 ° C. or higher and lower than 1250 ° C.
JP-A-9-111007 Japanese Patent Laid-Open No. 2004-156045

  However, heat treatment in an inert gas atmosphere is expensive in equipment, limited to a batch system because of complete sealing, productivity is reduced, and time and cost are required for the operation to replace the atmosphere with an inert gas. In operation, there is a problem that a running cost due to replenishment of replacement gas occurs.

  The present invention has been made in view of such conventional problems, and can be more easily maintained without heat treatment in an inert gas atmosphere having the various problems described above, and yet oxygen is not present. An object of the present invention is to provide a method for manufacturing a friction material that can achieve both prevention of a fade phenomenon, improvement in productivity, and reduction in production cost by heat treatment in an atmosphere.

  In order to achieve the above-mentioned object, the present inventors have continued intensive research, and if the water vapor obtained by evaporating water is heated to 100 ° C. or higher, it becomes superheated water vapor. A high-temperature superheated steam (referred to as “superheated steam” in the present specification) that was not conceivable in the past from 0 ° C. to less than 800 ° C. is obtained, and because 100% steam is used, the oxygen content is less than 0.3%. Therefore, it is found that oxidation by oxygen does not occur, and the friction material obtained by the heat treatment is smooth because the carbon content remains on the surface, so that a surface baking process using a gas burner is unnecessary. Based on this finding, the present invention has been achieved. Note that superheated steam is a concept that is obtained by heating and evaporating a substance that is liquid at room temperature to a temperature higher than its boiling point. Since it is sometimes referred to as “steam”, “superheated steam” is herein referred to as “superheated steam”.

That is, the present invention was able to solve the above problems by the following means.
(1) In the manufacturing method of the friction material which consists of a thermosetting resin binder, a reinforcing fiber, and a friction modifier, it heat-processes in a superheated steam atmosphere after thermoforming, The manufacturing method of the friction material characterized by the above-mentioned.
(2) In a method for producing a friction material comprising a thermosetting resin binder, a reinforcing fiber, and a friction modifier, the heat treatment is performed in heated air after thermoforming, and further in a superheated steam atmosphere. A method of manufacturing the material.
(3) The heat treatment in the superheated steam atmosphere is performed at a processing temperature of 180 ° C. or higher and lower than 800 ° C. for a processing time of 15 minutes to 1 hour, wherein the friction material according to (1) or (2) is manufactured. Method.

According to the present invention, the friction material is obtained by evaporating water with a heat source (electricity), further heating the water vapor to a boiling point or higher, forming superheated steam that is a transparent gas atmosphere of only water molecules, and thermoforming or further heat-treating with heated air. Can be heat-treated in a superheated steam atmosphere at 180 ° C. or higher and lower than 800 ° C. for 15 minutes to 1 hour to improve fade resistance and wear resistance.
In addition, heat treatment with superheated steam allows continuous heating, which is difficult with an inert gas, and there is no problem of variation in the actual temperature of the object to be processed in a batch system, a decrease in productivity, and the heat medium is water. Therefore, the running cost can be reduced as compared with the inert gas.
Furthermore, in the case of superheated steam, in addition to convective heat transfer, radiant heat transfer as a characteristic of water molecules also contributes, so the increase in the actual temperature of the friction material is significantly faster than air and inert gas, and in a short time. Heat treatment is possible.

  Embodiments of the present invention will be described below. The method for producing a friction material according to the present invention includes a raw material preparation step for preparing a raw material mixture by mixing raw materials mainly comprising a fiber base material, a thermosetting resin binder, and a filler, and a preliminary for pre-molding the raw material mixture. It includes a molding process, and a pressure heating molding process, a heat treatment process, a polishing process, and a coating process in which the preform obtained in the preforming process is subjected to pressure heating molding.

  The raw material used for the friction material can be selected from those usually used. Specifically, as the fiber base material, steel fibers, copper fibers, brass fibers and other metal fibers; aromatic polyamide fibers ( Aramid fiber, aramid pulp, etc .: commercially available products such as DuPont's product name Kevlar), flame-resistant acrylic fiber, acrylic pulp, organic fiber such as cellulose fiber; potassium titanate fiber, glass fiber, alumina fiber, carbon Non-asbestos-based inorganic fibers such as fibers, rock wool, and sepiolite fibers can be used. Among these, one kind or two or more kinds can be used in combination. Although the usage-amount of the whole fiber base material is not specifically limited, Preferably it is 5-50 mass% with respect to friction material whole quantity, More preferably, it is 10-45 mass%.

  The thermosetting resin binder has a role of bonding the blending components of the friction material, and phenol resin, melamine resin, epoxy resin, polyimide resin, or the like is used. Of these, a phenol resin is preferably used. Although the usage-amount of a thermosetting resin binder is not specifically limited, Preferably it is 5-20 mass% with respect to friction material whole quantity, More preferably, it is 10-20 mass%.

  Fillers include organic fillers such as resin dust (for example, cashew dust); metallic particles such as hard particles of metal oxides such as alumina, silica, zirconia, and chromium oxide, and metal particles such as copper, brass, and iron Fillers; scale-like inorganic substances such as vermiculite and mica; inorganic fillers such as inorganic compounds such as barium sulfate and calcium carbonate; solid lubricants such as graphite and molybdenum disulfide; and the like can be used. The blending amount of the filler is preferably 30 to 80% by mass, more preferably 40 to 80% by mass with respect to the total amount of the friction material.

  As a method of mixing each raw material described above, a dry method in which all raw material powders are directly and uniformly mixed, and all raw material powders are uniformly mixed and wetted in the presence of a solvent, and the resulting wet raw material mixture is dried. Although a wet method for preforming is known, any method may be used in the present invention. In the case of using a wet method, examples of the solvent include water, toluene, methanol, acetone, and methyl ethyl ketone. The method of uniformly mixing is not limited and can be performed by a commonly used known technique.

  In addition, a caking flocculant may be added and mixed while the raw materials are dry-mixed to wet the raw materials, and a wet raw material mixture for granulation into granules in the preforming step described below can be prepared. The caking flocculant used here is preferably a water-alcohol mixed solvent and the like, and as the alcohol, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, ethylene glycol, diethylene glycol and the like are used.

  The raw material mixture thus obtained is then preformed, for example, in the form of a tablet in a preforming step, and a preformed product to be subjected to a hot press or the like in the next pressure heating molding step is obtained. When using a raw material mixture containing an adhesive flocculant, it is granulated into granules, which are directly subjected to pressure heating molding as a preformed product, or the granules are further preformed again into tablets and the like and then pressed A method of subjecting to heat molding can also be taken. The preforming can be normally performed at normal temperature and a surface pressure of 5 to 50 MHz.

The present invention is characterized in that the heat treatment is performed in a superheated steam atmosphere as a manufacturing method thereof. In general, the superheated steam simply refers to steam higher than 100 ° C., but here, superheated steam higher than 100 ° C. at atmospheric pressure is targeted, and the oxygen concentration is less than 1% as dissolved oxygen.
Water is evaporated by a heat source (electricity), the water vapor is heated to the boiling point or higher, and the superheated steam is a transparent gas atmosphere containing only water molecules, and the friction material heat-formed or further heat-treated with heated air is used in the superheated steam atmosphere. By performing heat treatment at 180 ° C. or higher and lower than 800 ° C. for 15 minutes to 1 hour, fade resistance and wear resistance can be improved. More preferably, the heat treatment temperature is 300 to 450 ° C. in the above temperature range in consideration of organic dust having a small residual carbon ratio due to heat treatment, gasification of organic fibers, and deterioration of the adhesive bonding the friction material and the metal plate. preferable.

Furthermore, in the case of superheated steam, in addition to convective heat transfer, radiant heat transfer as a characteristic of water molecules also contributes, so the increase in the actual temperature of the friction material is significantly faster than air and inert gas, and in a short time. Heat treatment is possible. In addition, since the superheated steam in the present invention does not coexist with liquid water, it does not need to be under pressure and is irrelevant to the critical state. Since it can also be set to temperature, it can be set to the temperature below 800 degreeC.
Also, in the process of heat treatment with superheated steam, the work can be performed by blowing the superheated steam obtained by heating the steam and raising the temperature onto the friction material, so that the atmosphere is sealed so as not to escape. Therefore, the heat treatment apparatus is simplified, and expensive atmosphere gas replenishment is not required.

  The treatment temperature in the heat treatment step is preferably from 180 to less than 800 ° C, more preferably from 300 to 450 ° C. The curing temperature of the thermosetting resin is 180 ° C. for resins other than phenolic resins having a two-stage peak (140 ° C. and 250 ° C.), so that the heat treatment merit of superheated steam must be 180 ° C. ( If the temperature exceeds 800 ° C., it is not preferable from the viewpoint of gasification of organic dust and organic fibers, deterioration of the adhesive bonding the friction material and the metal plate, and heat cost. Further, if the treatment time is 15 minutes or less, there is no merit of heat treatment using superheated steam, while if it exceeds 1 hour, there is a disadvantage in terms of productivity and heat cost.

Hereinafter, the present invention will be described more specifically with reference to Examples 1 to 3 and Comparative Examples.
Examples and Comparative Examples The blending ratios (parts by mass) of the friction material materials used in Examples 1 to 3 and Comparative Examples are as shown below.
Phenolic resin 15
Aramid pulp 10
Inorganic fiber 15
Zirconium silicate 3
Organic dust 7
Barium sulfate 45
Scale-like graphite 5

Moreover, the process of Examples 1-3 and a comparative example is shown in FIG. A comparative example performs the processing process in the manufacturing method of the conventional friction material, The surface baking process is provided after the heat treatment process or the polishing process, and this surface baking process is 400-700 degreeC using a gas burner. The surface of the friction material is baked for about 1 minute, and is used to suppress the fade phenomenon. After this surface baking step, the surface of the friction material becomes lumpy with heat.
Table 1 shows the friction performance test results of the friction materials manufactured according to Examples 1 to 3 and the comparative example. In the examples, carbon remained on the surface of the friction material after the heat treatment with superheated steam and was smooth.

  From the friction performance test results shown in Table 1, it was confirmed that the fading property was improved by heat treatment with superheated steam. That is, the numerical value of the first fade does not decrease when the friction performance test is taken, and is stable. In the embodiment, even if the surface baking step is not provided, the surface baking step can be omitted because the fading property is improved.

It is a flowchart which shows the main manufacturing process of the friction material of the Example and comparative example of this invention.

Claims (3)

  In the manufacturing method of the friction material which consists of a thermosetting resin binder, a reinforcing fiber, and a friction adjustment material, it heat-processes in a superheated steam atmosphere after thermoforming, The manufacturing method of the friction material characterized by the above-mentioned.   In a method for producing a friction material comprising a thermosetting resin binder, a reinforcing fiber, and a friction modifier, a heat treatment is performed in heated air after thermoforming and further in a superheated steam atmosphere. Method.   The method for producing a friction material according to claim 1 or 2, wherein the heat treatment in the superheated steam atmosphere is performed at a processing temperature of 180 ° C or higher and lower than 800 ° C for a processing time of 15 minutes to 1 hour.

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